Method and device for measuring concentration of substance in fluid

ABSTRACT

A method and device for measuring a substance&#39;s concentration in a fluid. The method includes first passing a sample to be measured through a chemical sensor at least twice and recording the response value each time; forming a simultaneous equation set using the equation relation between the response value obtained during each measurement and the concentration of the substance, and the mass equation relation satisfied by the concentration change caused by a physical, chemical reaction during each measurement and by the change of the mass, electric quantity, and heat; solving for the concentration of the substance measured and the sensor calibration parameter. The method, used as an absolute measurement method, can be applied to calibrate the sample concentration of a fluid, overcomes the effects on the measurements caused by temperature, humidity, pressure, and some interfering gas, requires no sensor calibration, and substantially enhances the measurements&#39; stability and reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is divisional of co-pending U.S. patent applicationSer. No. 14/408,526, filed Dec. 16, 2014, U.S. Pat. No. 9,970,894 (May15, 2018), which is a national phase entry under 35 U.S.C. § 371 ofInternational Patent Application PCT/CN2013/000718, filed Jun. 20, 2013,designating the United States of America and published as InternationalPatent Publication WO2013/189175 A1 on Dec. 27, 2013, which claims thebenefit under Article 8 of the Patent Cooperation Treaty to ChinaApplication Serial Nos. 201210207872.6, filed Jun. 21, 2012, and201210224156.9, filed Jun. 29, 2012, the contents of the entirety ofeach of which are incorporated herein by this reference.

TECHNICAL FIELD

The application relates to a method and a device for measuring materialconcentration in a fluid, which can be used as an absolute measurementmethod for calibrating the concentration of a gas/liquid sample.

BACKGROUND

A method for measuring the material concentration C₀ with a chemicalsensor is based on a measurement equation of the response signal S₀:

S=f(C0; k0, k1 . . . kp−1)   (1)

Wherein, the parameters k_(j) depend on the structural properties of thesensor, the composition of the sample, and the temperature, pressure,and flow state of the sample and environment. The current signal S ofthe most commonly used electrochemical, semiconductor, andcatalyst-based sensor usually meets the following measurement equation:

S=kC ₀ +k ₀   (2)

Wherein, parameters k₀ and k are zero point and sensitivity parameter ofa sensor, respectively.

In the actual application of a sensor, the response signal of the sensormay be affected by factors such as the gas flow rate, pressure,temperature, and humidity, and other gas components, and the sensitivityof the sensor may vary owing to ageing, inactivation, activation, orpoisoning, etc. Therefore, a sensor usually has to be calibrated with atleast two standard samples with known concentration under conditionsclose to the actual application conditions, including gas flow rate,pressure, temperature, humidity, and gas components before it can beused, in order to ascertain the applicability of the equation (1) andthe parameters k_(j) of the sensor; in addition, the time of calibrationshould be close to the time of measurement as far as possible, to avoidthe interferences described above.

In actual application, the calibration process involves a series ofproblems, for example, there are technical and safety risks, since it isdifficult to prepare, store, carry or use calibration samples with lowconcentration, high volatility, high reactivity, and high hazards(toxic, harmful, flammable, and explosive); there are risks related withreliability and effectiveness, since it is usually difficult to simulatethe actual situation with the calibration sample and calibrationconditions; even though the actual situation can be simulated in thecalibration process, it is difficult to carry out calibration at thesite of application; even though the calibration can be carried out onsite, many user usually neglect calibration.

For example, it is difficult to obtain or use calibration samples oforganic volatile materials, such as formaldehyde and benzene, etc. It isdifficult to carry out calibration on site even in the industrial andenvironmental safety monitoring field where on-site calibration isapplied most widely, especially at coal and oil gathering andtransportation sites. Safety accidents incurred by misreport orconcealment often occur owing to negligence or improper calibration.Especially, in the civilian field, such as blood glucose test and indoorgas leakage warning, etc., in household application, calibration isseldom carried out, and the resulting accidents are often reported.

At present, efforts made to solve that problem mainly involve providingsafe, convenient, and reliable automatic calibrators. For example, inrecent years, Honeywell disclosed a number of patents related withsensor calibration and automatic calibration methods (U.S. Pat. No.7,975,525B2, U.S. Pat. No. 7,661,290B2, US2006/0266097A1,US2005/0262924A1, U.S. Pat. No. 7,401,493B2, U.S. Pat. No. 7,581,425B2,U.S. Pat. No. 7,655,186B2, U.S. Pat. No. 7,071,386B2, U.S. Pat. No.6,918,281, US2006/0042351A1), and Drager has disclosed several patentsrelated with sensor calibration (U.S. Pat. No. 7,704,356B2, U.S. Pat.No. 7,645,362B2) lately a common characteristic of these patents is thata standard gas is required, while only the method for producing thestandard gas varies among these patents. Is there any calibration methodthat doesn't require a standard gas?

In 1987 and 1989, City Tech and Drager, respectively, disclosed patents(U.S. Pat. No. 4,829,809, U.S. Pat. No. 4,833,909) in which calibrationcould be carried out without a calibration sample, an electrochemicalsensor is placed in an enclosed container filled with a sample, the gasconcentration is ascertained through coulomb electrolysis after thetested material is completely electrolyzed, and thereby the sensor iscalibrated.

In 2000, Industrial Scientific discloses a patent (U.S. Pat. No.6,055,840), in which a method for determining the gas concentration byregulating and controlling the resistance in a gas diffusion channelquantitatively was described. However, that method is also inconvenientto use in actual application, because the diffusion coefficient of thetested gas and at least one physical dimension of a gas diffusionchannel must be known.

These methods still belong to methods for laboratory research oranalysis, and are difficult to use in actual application. At present,the calibration of gas sensors still rely on a calibration method inwhich materials with standard concentration provided by a standardmeasurement department are used.

BRIEF SUMMARY

In view of the drawbacks in the prior art, the disclosure puts forward amethod and a device for measuring the absolute value of materialconcentration in a fluid, which utilize the intrinsic characteristics ofa sensor and physical and chemical laws, and don't have to use standardmaterials to calibrate the characteristics of the sensor.

The method can be expressed as follows:

Driving a sample to be tested to pass through a chemical sensor at leasttwice, and logging the response value of the chemical sensor in eachtime; establishing a simultaneous system of equations from themeasurement equation relationship between the response signal of thesensor obtained in each measurement and the concentration of the sampleand the mass equation relationship between the concentration change ofthe sample resulted from physical and chemical reactions in eachmeasurement and the change of mass, electric quantity, and heat, andsolving the simultaneous system of equations to ascertain theconcentration of the tested sample and the calibration parameters of thesensor.

When an electrochemical sensor is used in the measurement, the methodcan be expressed as:

Driving a sample to be tested to pass through an electrochemical sensorat least twice, and logging the response value of the electrochemicalsensor in each time; establishing a simultaneous system of equationsfrom the measurement equation relationship between the current value ofthe electrochemical sensor obtained in each measurement and theconcentration of the sample and the mass equation relationship betweenthe concentration change of the sample resulted from electrolysis andthe consumed electric quantity, and solving the simultaneous system ofequations to ascertain the concentration of the tested sample and thecalibration parameters of the sensor.

A device that implements the measurement method described above consistsof a sample chamber, an electrochemical sensor, a pump, and a valve,when the device is used for analysis of gas concentration, the samplechamber, electrochemical sensor, pump, valve, and a pipeline form acirculating flow path; the sample chamber is a slender pipeline, inwhich a gas flows in a manner of piston flow in the process of analysis,the volume of the sample chamber is greater than 95% of the total volumeof the circulating flow path, and the sample chamber is used to storethe fluid sample to be analyzed; the electrochemical sensor is enclosedin the circulating flow path, and is used to measure a response signaland electrolyze the electrochemical active component to be measured; thepump is used to drive the fluid to circulate in the circulating flowpath, so that the fluid can pass through the sensor at least twice.

Another device that implements the measurement method described aboveconsists of a piston sample chamber, a three-way valve, anelectrochemical sensor, and a buffer chamber, wherein, the piston samplechamber, three-way valve, electrochemical sensor, and buffer chamber areconnected in series through a pipeline, and one way of the three-wayvalve is used to receive a sample to be analyzed; the piston samplechamber is used to store the fluid to be analyzed and drive the fluid toflow to and fro in the pipeline and the sensor at a constant flow rate;the electrochemical sensor is used to measure a response signal andelectrolyze the electrochemical active component to be measured; thebuffer chamber is used to store the fluid.

In another method disclosed in the disclosure, the zero point of asensor is obtained by measurement, specifically, the method driving asample to be tested to pass through an electrochemical sensor at leasttwice, and logging the response current value of the electrochemicalsensor in each time, wherein, one of the two measurements is used tomeasure the zero point of the sensor; establishing a simultaneous systemof equations from the measurement equation relationship between thecurrent value of the electrochemical sensor obtained in each measurementand the concentration of the sample and the mass equation relationshipbetween the concentration change of the sample resulted fromelectrolysis and the consumed electric quantity, and solving thesimultaneous system of equations to ascertain the concentration of thetested sample and the calibration parameters of the sensor.

To implement the method described above, the disclosure discloses thefollowing four types of devices.

A device that implements the measurement method described above consistsof a sample chamber, a small gas chamber, an electrochemical sensor, apump, and a valve, wherein, the sample chamber, electrochemical sensor,pump and valve are connected through a pipeline to form a circulatinggas path, in the circulating gas path, the electrochemical sensor isconnected with the pump in series, the small gas chamber is connected inparallel via the valve at the other end of the pump and the other end ofthe electrochemical sensor, and the volume of the small gas chamber issmaller than 1/10 of the volume of the sample chamber; the samplechamber is a slender pipeline, the volume of the sample chamber isgreater than 95% of the total volume of the circulating gas path, a gasflows in the sample chamber in a manner of piston flow in the process ofanalysis, and the sample chamber is used to store the fluid sample to beanalyzed; the electrochemical sensor is enclosed in the circulating flowpath, and is used to measure a response signal and electrolyze theelectrochemical active component to be measured; the pump is used todrive the fluid to circulate in the circulating flow path, so that thefluid can pass through the sensor at least twice.

Another device that implements the measurement method described aboveconsists of a sample chamber, a capillarity tube, an electrochemicalsensor, a pump, and a valve, wherein, the sample chamber,electrochemical sensor, pump and valve are connected through a pipelineto form a circulating gas path; the sample chamber is a slenderpipeline, in which a gas flows in a manner of piston flow in the processof analysis, the volume of the sample chamber is greater than 95% of thetotal volume of the circulating gas path, and the sample chamber is usedto store the fluid sample to be analyzed; the electrochemical sensor isenclosed in the circulating flow path, the gas inlet and gas outlet thatcommunicate with the sensor are provided by the capillarity tube, theratio of the cross-sectional area to the length of the capillarity tubeis smaller than 5% of the ratio of the apparent area of poles of thesensor to the thickness of the gas chamber; the electrochemical sensoris used to measure a response signal and electrolyze the electrochemicalactive component to be measured; the pump is used to drive the fluid tocirculate in the circulating flow path, so that the fluid can passthrough the sensor at least twice.

Yet another device that implements the measurement method describedabove forms a circulating flow path consisting by a sample chamber, afilter, an electrochemical sensor, a pump, and a valve, wherein, thesample chamber, electrochemical sensor, pump and valve are connectedthrough a pipeline to form a circulating gas path, the filter isconnected in parallel via the valve in front of the gas inlet of thesensor in the pipeline; the sample chamber is a slender pipeline, a gasflows in the sample chamber in a manner of piston flow in the process ofanalysis, the volume of the sample chamber is greater than 95% of thetotal volume of the circulating gas path, and the sample chamber is usedto store the fluid sample to be analyzed; the electrochemical sensor isenclosed in the circulating flow path, and is used to measure a responsesignal and electrolyze the electrochemical active component to bemeasured; the pump is used to drive the fluid to circulate in thecirculating flow path, so that the fluid can pass through the sensor atleast twice.

Still another device that implements the measurement method describedabove consists of a first sample chamber, a second sample chamber, anelectrochemical sensor, pumps, and valves, wherein, the first samplechamber, electrochemical sensor, a pump and a valve are connectedthrough a pipeline to form a first circulating gas path; the secondsample chamber, a filter, a pump and a valve are connected through apipeline to form a second circulating gas path, and the two circulatinggas paths are connected in parallel with each other; the sample chamberis a slender pipeline, the volume of the sample chamber is greater than95% of the total volume of the circulating gas path, a gas flows in thesample chamber in a manner of piston flow in the process of analysis,and the sample chamber is used to store the fluid sample to be analyzed;the electrochemical sensor is enclosed in the circulating flow path, andis used to measure a response signal and electrolyze the electrochemicalactive component to be measured; the pump is used to drive the fluid tocirculate in the circulating flow path, so that the fluid can passthrough the sensor at least twice.

The method is an absolute concentration measurement method, and itovercomes the effect of temperature, humidity, pressure, and someinterfering gas to the measurement, and doesn't require calibration ofthe sensor, thus, it greatly improves the stability and reliability ofthe measurement.

With the device described above, the zero point of the sensor can bemeasured directly on site; thus, it is unnecessary to carry out zerocalibration for the sensor with zero gas before the measurement,therefore, the measuring process is simplified, the data processingcomplexity is decreased, a stage of error propagation is eliminated, andthereby the reliability and repeatability of the measurement result arefurther improved.

BRIEF DESCRIPTION OF THE DRAWINGS

To make the content of the disclosure understood more clearly, hereunderthe disclosure will be further detailed according to some embodiments,with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic structural diagram of the device in embodiment 1of the disclosure;

FIG. 2 is a schematic structural diagram of the device in embodiment 2and 5 of the disclosure;

FIG. 3 is a schematic structural diagram of the device in embodiment 3of the disclosure;

FIG. 4 is a schematic structural diagram of the device in embodiment 4of the disclosure;

FIG. 5 is a schematic structural diagram of the device in embodiment 6of the disclosure;

FIG. 6 is a diagram of comparison between measured value obtained withthe method disclosed in the disclosure and the actual concentration ofgas.

Among the figures: 1—first valve, 2—second valve, 3—third valve,4—fourth valve, 5—first pump, 6—electrochemical sensor, 7—samplechamber, 8—small gas chamber, 9—second pump, 10—third pump, 11—secondfilter, 12—second sample chamber, 13—piston sample chamber, 14—three-wayvalve, 15—electric buffer chamber, 16—filter.

DETAILED DESCRIPTION Embodiment 1

Please see FIG. 1.

The device consists of a sample chamber 7, an electrochemical sensor 6,a first pump 5, a second pump 9, and a first valve 1, a second valve 2,a third valve 3, and a fourth valve 4, wherein, the sample chamber 7,electrochemical sensor 6, first pump 5, and first valve 1, second valve2, third valve 3, and fourth valve 4 are connected through a pipeline toform a closed circulating flow path; the pipeline is composed ofcapillary tubes, and the internal volume of the capillary tube issmaller than 5% (equal to 4%) of the total volume of the circulatingflow path; the sample chamber 7 is constructed in a way that a gas flowsin it in a manner of piston flow in the process of analysis, the samplechamber 7 is a slender pipeline in structure, and the total volume ofthe sample chamber 7 is greater than 95% (equal to 96%) of the totalvolume of the circulating flow path; the electrochemical sensor isenclosed in the circulating flow path, and is used to measure a responsesignal and electrolyze the electrochemical active component to bemeasured; the pump is used to drive the gas to circulate in thecirculating gas path, and the flow rate of the circulating gas can beobtained from the volume of the gas chamber and the cycle period; asmall gas chamber 8 connected in parallel with the first pump 5 besidethe electrochemical sensor 6, third valve 3, and fourth valve 4 are usedto measure the zero point of the sensor on site, and the volume of thesmaller gas chamber 8 is smaller than 1/10 of that of the sample chamber7.

The actual measurement process is carried out through the followingthree steps:

(1) Sampling: switch the first valve 1 and second valve 2, and pump agas with the second pump 9 via the first valve 1, sample chamber 7,second valve 2 and second pump 9 into the sample chamber 7.

(2) Circulation and measurement: switch the first valve 1, second valve2, third valve 3, and fourth valve 4 and start the first pump 5 at thesame time, so that the gas flows through the first pump 5,electrochemical sensor 6, fourth valve 4, second valve 2, sample chamber7, first valve 1, second valve 2, returns to the electrochemical sensor6, and circulates in that way, when sample under the action of thecirculating pump, and carry out analysis and measurement in twocirculations, wherein, the gas is electrolyzed when it passes throughthe sensor, and the measurement equation met by the response value ofthe sensor whenever the gas passes through the sensor can be expressedas:

i ₀ =kC ₀ k ₀   (2)

i ₁ =kC ₁ +k ₀   (3)

Wherein, i₀ and i₁ are response values of the sensor in the twomeasurements, k is the sensitivity of the sensor, k₀ is the backgroundcurrent of the sensor, C₀ and C₁ are initial concentration of the sampleand concentration of the sample measured in the second measurement,respectively; the unknown quantities are k, k₀, C₀, and C₁.

According to Faraday's law, the mass equation of the relationshipbetween the quantity of sample consumed by electrolysis and theresultant change of concentration of the sample in each measurementcarried out by the sensor can be expressed as:

nFV(C ₁ −C ₀)=i ₀ *t   (4)

Wherein, n is the number of electronics involved in the reaction, F isFaraday constant, V is the volume of the sample chamber, and t is thecycle period.

(3) Measurement of zero point: after twice measurements are completed,switch the solenoid valves 3 and 4 to change the gas flow direction to5, 6, 4, 8, 3 and 5, in this case, the sensor carries out exhaustiveelectrolysis of the active gas component in the small circulating gaspath, and the response value of the sensor will approach to the zeroresponse value k₀ of the sensor after a period that is long enough.

Thus, the sample concentration C₀ and the sensor sensitivity k can besolved from the simultaneous equations (2), (3), (4) and directlymeasured k₀.

It is seen from this embodiment: the method can be used to directlyascertain the concentration of the measured material, withoutcalibrating the sensor before the measurement; in addition, thecalibration parameters (e.g., sensitivity and background current) of thesensor can be directly solved with the method. Since the sensorcalibration parameters are calculated in an actual measurement process,the method can be regarded as a self-calibration method. In addition,since the method utilizes the difference between two response values ofthe sensor, the contributions of temperature, pressure, flow, andinterfering materials, which are identical in each measurement, isdeducted, therefore, compared with the conventional method, whichutilizes signals that contain these contributing factors, the method hashigher sensitivity, selectivity, and stability.

The implementation of the method has requirements for gas pathstructure, gas path resistance and sensor sensitivity. Generallyspeaking, the resistance in the bigger circulating gas path and theresistance in the smaller circulating path must be essentially equal toeach other, in order to ensure the gas flow rate in zero measurement isessentially equal to flow rate in the concentration measurement. Inaddition, two criteria must be met in the selection of sensitivity ofthe sensor, on the one hand, the sensitivity must be appropriate (nottoo high or too low), to ensure that the change of concentrationgradient resulted from each circulation cycle of the gas in the majorcirculation and analysis process is distinguishable and theconcentration will not be decreased too severely after severalcirculation cycles; on the other hand, on the premise that the firstcriterion is met, the sensitivity should be high enough, so that theactive gas in the small circulating gas path can be depleted in a shorttime period.

Four valves are used in this embodiment to control the gas flowdirection and on/off. Apparently, the first valve 1 and third valve 3can be replaced with a two-position three-way valve, and the secondvalve 2 and fourth valve 4 can also be replaced with a two-positionthree-way valve, so as to reduce the elements in the gas path.

Embodiment 2

FIG. 2 shows a second gas path design that implements the measurementmethod disclosed in the disclosure. The device comprises a samplechamber 7, an electrochemical sensor 6, a first pump 5, a first valve 1,a second valve 2, a third valve 3 and a fourth valve 4, wherein, thesample chamber 7, electrochemical sensor 6, first pump 5, first valve 1and second valve 2 are connected through a pipeline to form acirculating gas path; the sample chamber 7 is a slender pipeline, inwhich a gas flows in a manner of piston flow in the process of analysis,the volume of the sample chamber is greater than 95% (equal to 98%) ofthe total volume of the circulating gas path, and the sample chamber 7is used to store the fluid sample to be analyzed; the electrochemicalsensor is enclosed in the circulating flow path, the gas inlet and gasoutlet that communicate with the sensor are provided by capillaritytubes, the ratio of the cross-sectional area to the length of thecapillarity tube is smaller than 5% (equal to 2%) of the ratio of theapparent area of poles of the sensor to the thickness of the gaschamber, the electrochemical sensor is used to measure a response valueand electrolyze the electrochemical active component to be measured; thepump 5 is used to drive the fluid to circulate in the circulating flowpath, so that the fluid can pass through the sensor at least twice.

The actual measurement process is carried out through the followingsteps:

(1) Sampling: adjust the state of the first valve 1, second valve 2,third valve 3 and fourth valve 4, and start the first pump 5 and secondpump 9, so that the gas passes through the first valve 1, sample chamber7, second valve 2 and second pump 9, and is collected into the samplechamber 7, the gas in the other way passes through the first valve 1,third valve 3, first pump 5, electrochemical sensor 6, fourth valve 4,second valve 2 and second pump 9, and flows out.

(2) Measurement of zero point: close the first valve 1, second valve 2,third valve 3 and fourth valve 4, and stop the first pump 5 and secondpump 9, and hold the gas for a while; in that state, the sensor keepsdepleting the active gas in the small gas chamber of the sensor byelectrolysis; after a time period that is long enough, the responsevalue of the sensor will be the zero response value.

(3) Circulation and measurement: after the zero response value isobtained, start the first pump 5 and adjust the state of the valves, sothat the gas circulates in the circulating gas path constituted by thesample chamber 7, first pump 5, electrochemical sensor 6, and samplechamber 7 to carry out a plenty of analysis cyclically.

The implementation of the method has requirements for gas path structureand sensor sensitivity, i.e., the volume of cavity in the sensor must besmall enough, the contact area between the gas electrodes of the sensorand the sample must be large enough, the gas inlet and gas outlet thatcommunicate with the sensor must be provided by capillary tubes, and theratio of the cross-sectional area to the length of the capillary must besmaller than 1% of the ratio of the apparent area of poles of the sensorto the thickness of the gas chamber. Thus, the gas diffusion process canbe neglected when there is no forced convection, and the sensor canaccomplish electrolysis of 99% of active component in a required timeperiod. The sensitivity of the gas sensor must be appropriate (not toohigh or too low), in order to ensure that the change of concentrationgradient resulted from each gas circulation cycle in the cyclic analysisprocess is distinguishable and the concentration will not be decreasedtoo severely after several circulation cycles. Of course, the gas inletand gas outlet that communicate with the sensor may not be implementedby means of capillary tubes; instead, the communication between thesensor and the gas path can be cut off by means of a solenoid valve inthe measurement of zero point.

Embodiment 3

FIG. 3 shows a third gas path design that implements the measurementmethod disclosed in the disclosure. The device forms a circulating flowpath by a sample chamber 7, a filter 16, an electrochemical sensor 6, afirst pump 5, a first valve 1, a second valve 2 and a third valve 3,wherein, the sample chamber 7, electrochemical sensor 6, first pump 5,first valve 1, second valve 2 and third valve 3 are connected through apipeline to form a circulating gas path; the filter is connected inparallel via the third valve 3 in front of the gas inlet of the sensorin the pipeline; the sample chamber 7 is a slender pipeline, a gas flowsin the sample chamber 7 in a manner of piston flow in the process ofanalysis, the volume of the sample chamber 7 is greater than 95% (equalto 99%) of the total volume of the circulating gas path, and the samplechamber 7 is used to store the fluid sample to be analyzed; theelectrochemical sensor is enclosed in the circulating flow path; thepump is used to drive the fluid to circulate in the circulating flowpath, so that the fluid can pass through the sensor at least twice.

The actual measurement process is carried out through the followingsteps:

(1) Sampling: switch the first valve 1 and second valve 2, and start thesecond pump 9, so that the gas passes through the first valve 1, samplechamber 7, second valve 2, and second pump 9, and is collected into thesample chamber 7;

(2) Circulation and measurement: switch the first valve 1 and secondvalve 2, and start the first pump 5, so that the gas circulates in thecirculating gas path constituted by the sample chamber 7, first pump 5,third valve 3, electrochemical sensor 6, and sample chamber 7 to carryout a plenty of analysis cyclically.

(3) Measurement of zero point: after a required number of measurementcycles are completed, switch the third valve 3 to change the gas flowpath to sample chamber 7, first pump 5, third valve 3, filter 16,electrochemical sensor 6 and sample chamber 7, so that the gas passesthrough the filter 16 before it flows through the sensor, in that state,the response current of the sensor is zero current after the activecomponent is filtered.

Embodiment 4

FIG. 4 shows a fourth gas path design that implements the measurementmethod disclosed in the disclosure. The device consists of a samplechamber 7, a second sample chamber 12, an electrochemical sensor 6, afirst pump 5, a first valve 1, a second valve 2, a third valve 3and afourth valve 4, wherein, the sample chamber 7, electrochemical sensor 6,first pump 5, first valve 1 and second valve 2 are connected through apipeline to form a first circulating gas path; the second sample chamber12, a second filter 11, a third pump 10, the third valve 3 and thefourth valve 4 are connected through a pipeline to form a secondcirculating gas path, and the two circulating gas paths are connected inparallel with each other; the sample chamber 7 is a slender pipeline,the volume of the sample chamber 7 is greater than 95% (equal to 99.5%)of the total volume of the circulating gas path, a gas flows in thesample chamber 7 in a manner of piston flow in the process of analysis,and the sample chamber 7 is used to store the fluid sample to beanalyzed; the electrochemical sensor is enclosed in the circulating flowpath, and is used to measure a response value and electrolyze theelectrochemical active component to be measured; the pump is used todrive the fluid to circulate in the circulating flow path, so that thefluid can pass through the sensor at least twice, the flow rate of thecirculating gas can be obtained from the volume of the gas chamber andthe cycle period.

The actual measurement process is carried out through the followingthree steps:

(1) Sampling: switch the first valve 1, second valve 2, third valve 3and fourth valve 4, so that the gas is pumped by the second pump 9through two ways into the sample chamber 7 and the second sample chamber12, i.e., in one way, the gas is pumped through the first valve 1,sample chamber 7, second valve 2 and second pump 9 into the samplechamber 7; in the other way, the gas is pumped through the first valve1, third valve 3, second sample chamber 12, fourth valve 4, second valve2 and second pump 9 into the second sample chamber 12.

(2) Circulation and measurement: switch the first valve 1 and secondvalve 2, and start the first pump 5 at the same time, so that the gassample in the sample chamber 7 circulates through the first valve 1,first pump 5, electrochemical sensor 6, second valve 2, and then returnsto sample chamber 7 under the action of the circulating pump, to carryout measurement and analysis in two circulation cycles.

(3) Measurement of zero point:

It is carried out in two steps: first, as the cyclic analysis isexecuted, switch the third valve 3 and fourth valve 4, and start thethird pump at the same time, so that the gas in the sample chamber 7flows through the third valve 3, first pump 5, second filter 11, fourthvalve 4, returns to the second sample chamber 12, and circulates in thatway under the action of the pump, since the element 11 is a filter forfiltering active substances, such as active carbon or potassiumpermanganate, etc., the active component is removed by absorption orreaction when gas flow passes through the filter; thus, the gasreturning to the sample chamber after a circulation cycle is zero gasafter the active component is filtered off.

After two measurement cycles are completed, switch the first solenoidvalve 1, second valve 2, third valve 3 and fourth valve 4, and start thefirst pump 5 to change the gas flow direction, so that the gas flowsthrough the second sample chamber 12, third valve 3, first valve 1,first pump 5, electrochemical sensor 6, third valve 3, fourth valve 4,and returns to the second sample chamber 12, and circulates in that way,in this state, the gas flowing in the pipeline is zero gas, and theresponse value of the sensor is zero response value.

Embodiment 5

Here the method and device for gas detection in the disclosure will bedescribed with reference to FIG. 2. The device consists of a samplechamber 7, an electrochemical sensor 6, a first pump 5, a first valve 1,a second valve 2, a third valve 3 and a fourth valve 4, wherein, thesample chamber 7, electrochemical sensor 6, first pump, first valve 1,second valve 2, third valve 3 and fourth valve 4 and pipeline forms aclosed circulating flow path; preferably, the pipeline is composed ofcapillary tubes, and the internal volume of the capillary tube issmaller than 5% of the total volume of the circulating flow path,optimally smaller than 1% of the total volume of the circulating flowpath; the sample chamber is constructed in a way that the gas flow in itis piston flow during cyclic analysis; preferably the sample chamber isa slender pipeline in structure, and the total volume of the samplechamber is greater than 95% of the total volume of the circulating flowpath, optimally greater than 99% of the total volume of the circulatingflow path; the electrochemical sensor is enclosed in the circulatingflow path, and is used to measure a response value and electrolyze theelectrochemical active component to be measured; the pump drives the gasto circulate in the circulating flow path, and the flow rate of thecirculating gas can be obtained from the volume of the gas chamber andthe cycle period.

To carry out analysis, the first step is sampling: the valves areopened, and the gas is pumped by externally connecting the second pump 9into the sample chamber, or, the sample can be directly fed into thesample chamber, so that the sample chamber is filled with the sample tobe tested.

Then, switch the first valve 1, second valve 2, third valve 3 and fourthvalve 4, and start the first pump 5 at the same time, the sample iselectrolyzed by the sensor in three circulation cycles under the actionof the circulating pump. The response value of the sensor whenever thegas passes through the sensor can be expressed with the followingmeasurement equation:

i ₀ =kC ₀ +k ₀   (3)

i ₁ =kC ₁ +k ₀   (4)

i ₂ =kC ₂ +k ₀   (5)

Wherein, i₀, i₁ and i₂ are response values of the sensor in themeasurement cycles, respectively, k is the sensitivity of the sensor, k₀is the background current of the sensor, C₀, C₁ and C₂ are initialconcentration of the sample, concentration of the sample measured in thesecond measurement cycle, and concentration of the sample measured inthe third measurement cycle, respectively, there are five unknownquantities: k, K₀, C₀, C₁, and C₂.

According to Faraday's law, the mass equation of the relationshipbetween the quantity of sample consumed by electrolysis and theresultant change of concentration of the sample in each measurementcycle carried out by the sensor can be expressed as:

nFV(C ₁ −C ₀)=i ₀ *t   (6)

nFV(C ₂ −C ₁)=i ₀ *t   (7)

Wherein, n is the number of electronics involved in the reaction, F isFaraday constant, V is the volume of the sample chamber, and t is thecycle period.

From the above five equations, the parameters, including sampleconcentration, sensor sensitivity, and background current, can besolved, without calibrating the sensor with a standard gas.

It is seen from this embodiment: the method can be used to directlyascertain the concentration of the measured material, withoutcalibrating the sensor before the measurement; in addition, thecalibration parameters (e.g., sensitivity and background current) of thesensor can be directly solved with the method. Since the sensorcalibration parameters are calculated in an actual measurement process,the method can be regarded as a self-calibration method. In addition,since the method utilizes the difference between two response values ofthe sensor, the contributions of temperature, pressure, flow, andinterfering materials, which are identical in each measurement, isdeducted. Therefore, compared with the conventional method, whichutilizes signals that contain these contributing factors, the method hashigher sensitivity, selectivity, and stability.

Though some examples of measurement with an electrochemical sensor aredescribed in above embodiments, the actual application is not limited tothose examples. If other types of sensors are used, such as sensors thatmeasure concentration by measuring the change of material mass or heat,the analytical method and device described above are also applicable,provided that the change of quantity in the process of measurement meetsthe mass equation and can be calculated.

An inducted mathematical representation of the method is given below:

1. A sample with concentration C₀ to be measured is measured by the samechemical sensor for n times successively. In the j^(th) measurement, theinlet concentration and outlet concentration of the sensor are C_(j−1)and C_(j), respectively, and the response value S_(j−1) follows themeasurement equation (1), i.e.:

S _(j−1) =F(C _(j−) , k ₁ , k ₂ . . . k _(m))j=1,2, . . . . , n   (8)

or

S _(j−1) −S _(j) =F(C _(j−1) , k ₁ , k ₂ . . . k _(m))−F(C _(j) , k ₁ ,k ₂ . . . k _(m))   (9)

FIG. 1 shows an example of successive cyclic measurement.

2. The concentration change of the tested material passing through thechemical sensor follows the following mass equation (see FIG. 1):

C _(j−1) −C _(j) =R(C _(j−1) , C _(j) , K ₁, K₂ . . . K _(p))/V   (10)

In above equation, R is the average consumption rate of the testedmaterial in the chemical sensor, wherein, K_(j) is a rate constant;K_(j) and V are stay time of the sample in the chemical sensor and thevolume of gas, respectively, and they are known design data.

The concentration C₀ of the measured material and the calibrationparameters can be ascertained by solving the simultaneous equations (9)and (10), wherein, the number of successive measurement n is determinedby the condition for a unique solution that meets the system ofequations (the number of independent equations is equal the number ofunknown quantities, i.e., 2n=(n+1)+m+p), i.e., it is the required numberof measurement.

n=m+p+1   (11)

Thus, by measuring the same sample for several times and solving thesystem of equations shown above, according to the correlation among themeasurement, the concentration of the tested sample and the calibrationparameter of the sensor used in the measurement can be calculated.

Embodiment 6

Hereunder another method and a device in the disclosure will bedescribed with reference to FIG. 5. The device consists of a pistonsample chamber 13, a three-way valve 14, an electrochemical sensor 6,and a buffer chamber 15, wherein, the piston sample chamber 13,three-way valve 14, electrochemical sensor 6, and buffer chamber 15 areconnected in series through a pipeline, and one way of the three-wayvalve 14 is used to receive a sample to be analyzed; the piston samplechamber 13 is used to store the fluid to be analyzed and drive the fluidto flow to and fro in the pipeline and the sensor at a constant flowrate; the electrochemical sensor is used to measure a response value andelectrolyze the electrochemical active component to be measured; thebuffer chamber 15 is used to store the fluid temporarily.

Sampling: switch the three-way valve 14 and pull the piston to collect asample to be analyzed.

First analysis: switch the three-way valve 14, and push the piston ofthe sample chamber at a fixed rate, so that the gas passes through theelectrochemical sensor 6 and buffer chamber 15, and the original gas inthe buffer chamber 15 is discharged, to log the response value of thesensor.

Second analysis: pull the piston of the sample chamber at the same rate,so that the sample gas passes through the buffer chamber 15 andelectrochemical sensor 6 and returns to the sample chamber, toaccomplish a second measurement cycle.

The above measurement can be carried out to and fro, to obtain arequired measurement and system of mass equations, so as to solve thesample concentration and sensor parameters.

In this embodiment, the buffer chamber 15 can be replaced with a gassample bag or a sample chamber with a movable piston.

The piston sample chamber 13 can be implemented by a combination ofpump, valve, and gas bag. The gas pumping direction can be switched bymeans of the valve, so that the gas to be analyzed flows to and frobetween the sample chamber and the buffer chamber.

Since there is no essential difference between liquid samples and gassamples in the analytical method, the method described in aboveembodiments is also applicable to analysis of liquid samples.

The following application example explains how to use the methoddisclosed in the disclosure to measure nitrogen oxide in the environmentor exhaled from human body.

This example explains how to use the disclosure to measure nitrogenoxide in the environment or exhaled from human body. As a marker ofairway inflammation, exhaled nitrogen oxide can be used to diagnose,keep track of, and monitor respiratory diseases, such as asthma. InEuropean and American countries, standards are established to encourageand recommend such non-intrusive diagnostic techniques, and thesestandards specify that the detection accuracy and lower limit should notbe inferior to 5 ppb. For detection at such a low concentration, thesensitivity of a gas sensor may have a quick and obvious drift, owing tothe effect of the ambient humidity and other interfering gasses. Morefrequent and professional calibration is required, when compared withdetection at higher concentrations.

For example, in patent US20040082872, high-sensitivity detection andanalysis of exhaled gas is realized by strictly controlling thetemperature (22° C.) and humidity (70%) of the sample gas and thetemperature (22° C.) of the gas sensor, and the drift of sensitivityincurred by temperature and humidity is decreased to some degree.However, a sensor will still have quick and obvious sensitivity driftafter it is used for many times, owing to the effect of otherinterfering gasses and ageing or inactivation of the detectingelectrodes, in that case, the sensor has to be replaced, or externalcalibration has to be carried out by specialists with the methodspecified by the manufacturer periodically (e.g., once in every 7 daysor once after a specified number).

In contrast, since the analytical method disclosed in the disclosurededucts the effect of zero and sensitivity drift of the sensor, it isunnecessary to calibrate the sensor, and it is unnecessary to controlthe measuring conditions like the case described in patent US20040082872at constant temperature and humidity values when the sensor is used fordetecting exhaled nitrogen oxide, thus, the measuring device issimplified, and the accuracy and reliability of measurement areimproved.

The testing device in this embodiment is shown in FIG. 3.

In the measurement process, NO gas samples are prepared at 10concentration levels (5, 10, 20, 40, 60, 80, 150, 200, 250 and 300 ppb)with a range of 5˜300 ppb from a standard gas, after the gas sample isfed into a sample chamber 7 and replace the original gas in the samplechamber 7 completely, the first valve 1 and second valve 2 are shut off,and the first pump 5 is started at the same time, to carry out cyclicelectrolysis. After the sample gas circulates in the pipeline and ismeasured for three cycles, the concentration of the sample gas iscalculated with an obtained curve. FIG. 5 shows the result obtainedafter three measurements are completed and the mean value of themeasurements is plotted against the concentration of the prepared gas,and a regression analysis is carried out. It can be seen from theresult: the result obtained with the method essentially matches theconcentration of prepared gas, and the linear dependence is 0.996 withinthe range of 5-300 ppb.

While the object, technical scheme, and beneficial effects of thedisclosure are detailed above in some embodiments, it should beunderstood that those embodiments are exemplary instead of constitutingany limitation to the disclosure, any modification, equivalentreplacement, or improvement made without departing from the spirit andprinciple of the disclosure shall be deemed as falling in the scope ofprotection of the disclosure.

What is claimed is:
 1. A device for measuring material concentration ina fluid, said device comprising: a sample chamber; an electrochemicalsensor; a valve; and a pipeline, wherein said device is configured tomeasure material concentration in a fluid.
 2. The device of claim 1,further comprising a pump.
 3. The device of claim 2, which consists of:the sample chamber, which stores a fluid sample to be analyzed; theelectrochemical sensor; the pump; the valve; and the pipeline, wherein,when the device is used for analysis of gas concentration, the samplechamber, electrochemical sensor, pump, valve, and pipeline form acirculating flow path; wherein the sample chamber is a slender pipeline,in which a gas flows in a manner of piston flow during analysis, whereinthe sample chamber has a volume greater than 95% of the total volume ofthe circulating flow path, wherein the electrochemical sensor isenclosed in the circulating flow path, and is used to measure a responsevalue and electrolyze a chemical active component to be measured; andwherein the pump drives the fluid to circulate in the circulating flowpath, so that the fluid can pass through the electrochemical sensor atleast twice.
 4. The device of claim 1, wherein the valve is a three-wayvalve, and which device consists of: a piston sample chamber; thethree-way valve; the electrochemical sensor; a buffer chamber; and thepipeline, wherein the piston sample chamber, three-way valve,electrochemical sensor, and buffer chamber are connected in seriesthrough the pipeline, and wherein one way of the three-way valve is usedto receive a sample to be analyzed; wherein the piston sample chamberstores fluid to be analyzed and drives the fluid to flow to and fro inthe pipeline and the electrochemical sensor at a constant flow rate;wherein the electrochemical sensor measures a response value andelectrolyzes an electrochemical active component to be measured; andwherein the buffer chamber is used to store the fluid.
 5. The device ofclaim 2, which consists of: the sample chamber; a small gas chamber; theelectrochemical sensor; the pump; the valve; and the pipeline, whereinthe sample chamber, electrochemical sensor, pump and valve, areconnected through the pipeline to form a circulating gas path, in whichthe electrochemical sensor is connected in series with the pump, whereinthe small gas chamber is connected in parallel via the valve at theother end of the pump and the other end of the electrochemical sensor,and wherein the volume of the small gas chamber is smaller than 1/10 ofthe volume of the sample chamber.
 6. The device of claim 5, wherein, thesample chamber is a slender pipeline, in which a gas flows in a mannerof piston flow in the process of analysis, the volume of the samplechamber is greater than 95% of the total volume of the circulating flowpath, and the sample chamber is used to store the fluid sample to beanalyzed; the electrochemical sensor is enclosed in the circulating flowpath, and is used to measure a response signal and electrolyze theelectrochemical active component to be measured; the pump is used todrive the fluid to circulate in the circulating flow path, so that thefluid can pass through the electrochemical sensor at least twice.
 7. Thedevice of claim 5, wherein, the pipeline is composed of capillary tubes.8. The device of claim 2, which consists of: the sample chamber; acapillary tube; the electrochemical sensor; the pump; the valve; and thepipeline, wherein the sample chamber, electrochemical sensor, pump, andvalve are connected through the pipeline to form a circulating gas path;wherein the electrochemical sensor is enclosed in the circulating flowpath, wherein the gas inlet and gas outlet that communicate with theelectrochemical sensor are provided by the capillary tube, and whereinthe ratio of the cross-sectional area to the length of the capillarytube is smaller than 5% of the ratio of the apparent area of poles ofthe electrochemical sensor to the thickness of the gas chamber.
 9. Thedevice of claim 2, which consists of: the sample chamber; a filter; theelectrochemical sensor; the pump; and the valve, wherein, the samplechamber, electrochemical sensor, pump and valve are connected throughthe pipeline forming a circulating flow path by the sample chamber,filter, electrochemical sensor, pump, and valve, wherein, the samplechamber, electrochemical sensor, pump and valve are connected throughthe pipeline to form a circulating gas path, and wherein the filter isconnected in parallel via the valve in front of the air inlet of theelectrochemical sensor in the pipeline.
 10. The device of claim 2, whichconsists of: the sample chamber; a second sample chamber; theelectrochemical sensor; the pump; and valves, wherein the samplechamber, electrochemical sensor, pump and a valve are connected throughthe pipeline to form a first circulating gas path, wherein the secondsample chamber, a filter, the pump and a valve are connected through thepipeline to form a second circulating gas path, and wherein the twocirculating gas paths are connected in parallel with each other.
 11. Thedevice of claim 8, wherein: the sample chamber is a slender pipeline, inwhich a gas flows in a manner of piston flow in the process of analysis,the volume of the sample chamber is greater than 95% of the total volumeof the circulating flow path, the sample chamber is used to store thefluid sample to be analyzed, the electrochemical sensor is enclosed inthe circulating flow path, and measures a response signal andelectrolyzes the electrochemical active component to be measured, andthe pump drives the fluid to circulate in the circulating flow path, sothat the fluid can pass through the electrochemical sensor at leasttwice.
 12. The device of claim 8, wherein, the pipeline is composed ofcapillary tubes.
 13. The device of claim 9, wherein: the sample chamberis a slender pipeline, in which a gas flows in a manner of piston flowin the process of analysis, the volume of the sample chamber is greaterthan 95% of the total volume of the circulating flow path, the samplechamber is used to store the fluid sample to be analyzed, theelectrochemical sensor is enclosed in the circulating flow path, andmeasures a response signal and electrolyzes the electrochemical activecomponent to be measured, and the pump drives the fluid to circulate inthe circulating flow path, so that the fluid can pass through theelectrochemical sensor at least twice.
 14. The device of claim 9,wherein, the pipeline is composed of capillary tubes.
 15. The device ofclaim 10, wherein: the sample chamber is a slender pipeline, in which agas flows in a manner of piston flow in the process of analysis, thevolume of the sample chamber is greater than 95% of the total volume ofthe circulating flow path, the sample chamber is used to store the fluidsample to be analyzed, the electrochemical sensor is enclosed in thecirculating flow path, and measures a response signal and electrolyzesthe electrochemical active component to be measured, and the pump drivesthe fluid to circulate in the circulating flow path, so that the fluidcan pass through the electrochemical sensor at least twice.
 16. Thedevice of claim 10, wherein, the pipeline is composed of capillarytubes.